Sidmouth thatch-fire warning

PUBLISHED: 10:33 30 October 2009 | UPDATED: 10:53 18 June 2010

Sidmouth is an area of outstanding beauty and also home to a number of thatched properties contributing to its charm.

Sidmouth is an area of outstanding beauty and also home to a number of thatched properties contributing to its charm.

Devon & Somerset Fire & Rescue Service are concerned that owners of thatched properties take steps to reduce the chance of an emergency relating to fire occurring. Fire in thatch is not an inevitable occurrence but it is an organic material, subject to different behaviour patterns depending on its surroundings, treatments and choice of materials or styles. It has a finite life span, measured in tens rather than hundreds of years. And above all it is combustible.

Fire in a thatched roof often starts inside the thatch it is difficulty to detect and once started is almost impossible to control. Once a fire has taken hold within a roof it will spread rapidly, due to the very nature of how thatch burns and detection is often too late and invariably devastating! A thatched home can be ruined not only by the fire but by the amount of water needed to put it out, within an ancient cottage water can dissolve old cobb walls as well as causing serious water damage throughout.

Every year, over 50 historic thatched buildings out of an estimated stock of 24,000 listed properties are destroyed and lost through preventable fires "mysteriously" breaking out in the thatch. The reason has been understood for a number of years, but still the losses remain constant. This year there have already been 77 serious thatch fires throughout the UK, damage to property is extensive and devastating although risk to life is very low.

Many of the thatch fires are chimney-related. Modern enclosed solid fuel appliances are designed to burn efficiently and cleanly, often flues pass through old chimneys, where there is only a four-inch thickness of brick, which makes the thatch especially vulnerable to the risk of heat build-up and eventually combustion at a point between the brick and the thatch.

The danger zone for heat transfer and thatch ignition, is associated with older and/or listed properties with any two or more of the conditions highlighted below:

* A deep multi-layer thatch where the thatch is over one metre deep-a guide to the depth of thatch can be assessed in relation to the level of visible chimney

* Originally chimney height would have been about two metres from the ridge.

* Regular use of a multi-fuel or wood burning stove or an open fire with an inappropriate, old or poorly fitted liner

* Central chimney surrounded by thatch or a house that is part of a terrace

* A blocked or tarry spark arrestor will increase the risk associated with the points above

* Electrical faults and careless workmen, any recessed halogen spot lights, those particularity in bedroom or bathroom ceilings

* Security Lights - situated too close to the eaves. Any outside lights, particularly those fitted with motion sensors should be installed at least 1 metre away from any thatch

* Discarded cigarettes and garden bonfires

* Television aerials on thatched buildings should be fitted to a freestanding pole. Where this is not possible, the aerial should be fixed to a gable or gable-end chimney, where the cable can be run down the wall, avoiding contact with the thatch. Disconnect your television aerial during electrical storms to prevent damage to the system

Marjorie Saunders, National Society of Master Thatchers said "Fires in thatched properties are relatively rare but when they do occur the consequences are devastating. The principal causes and mechanisms of fire spread are understood, nevertheless once a fire occurs it is almost impossible to control.

"Preventing the destruction of thatched buildings by fire, particularly those that are listed and of historic importance is the greatest conservation task facing the industry today. It is essential that owners of thatched properties understand the risks from fire associated with thatch, fire prevention is all about managing the risk.

"Fortunately, local fire and rescue services, conservation officers, thatchers and specialist thatch insurers have the necessary knowledge to provide free advice and guidance; owners only have to ask."

Wood burning stoves

The increased efficiency of such stoves, whilst very welcome to residents of otherwise draughty older properties, has its own implications with regard to fire risk. Such efficiency depends on a high flue gas temperature of around 500°C which is concentrated in a narrow air column. When installed in a properly regulated, modern chimney this type of system is a highly effective way of getting maximum heat out of burning wood; but where ancient chimney stacks are concerned, the inappropriate introduction of such installations, with metal liners can create serious problems.

Research carried out in the1990s indicates that in a single-skinned brick chimney, heat can migrate into the deep thatch surrounding the stack and needs only to reach 200°C for charring of the thatch in contact to commence. And while this may not happen immediately, it must be remembered that the process of lighting and extinguishing the stove takes place on a regular basis year in, year out and because of the excellent insulating properties thatch the temperature does not drop to ambient in between lighting and extinguishing the stove.

If the use of such stoves is to be contemplated in an old thatched house, it is essential that a concrete of pumice insulated liner be inserted to isolate the hot gases from the surrounding brickwork. It is also essential that such lining is carried out by a properly qualified installer to ensure that it runs centrally without coming into contact with the chimney interior, that there are no gaps in concrete segment liners and that it runs the entire length of the stack. The most popular of liners is either flexible metal or of a double skin metal construction, this type of liner is not recommended, the void around the pipe work must be backfilled with the recommended insulation material to avoid intense heat bridging the gap.

Traditionally, combed wheat reed and long straw thatch is repaired or maintained by fixing new coats over older layers, in Devon water reed thatch can also be spar coated in a manner similar to combed wheat reed. The depth of thatch increases over the years, and where the thatch abuts the chimney can easily reach depths of 1-2 metres. In this way, a considerable surface area builds up against the chimney making the thatch more vulnerable.

It is the combination of deep thatch and a central chimney in conjunction with the use of multi-fuel stoves that put properties most at risk.

If in doubt, ask and don't use any chimney related appliance until you are SURE it is safe!

In addition to following all the usual precautions for fire safety in the home (see the link below for these everyday safety measures), if you are in a thatched building, you should also:

* keep chimneys and flues clean and well-maintained

* use a bulkhead type light fitting in your loft space

* never burn rubbish or garden waste near the property

* never light fireworks or barbeques near a thatched property

To request a Home Safety Visit call free on: 0800 73 11 822. For other fire safety advice, contact the Devon & Somerset Fire & Rescue Service Helpline on: 01392 872288 or visit our website www.dsfire.gov.uk


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